£20m compensation for botched basement work

London's mania for digging out deep basements has led to a flood of claims against builders who have botched the job of creating new subterranean living space.

More than £20 million has been paid out for damage to 890 homes since 2005, according to new industry figures, with the annual figure rising 60 per cent to a record of almost £5 million last year.

The biggest single “basement nightmare” claim was for almost £500,000. The average is about £24,000.

The problem is expected to get worse as basements get bigger and more complex with homeowners demanding swimming pools, gyms, cinemas and squash courts under their houses.

Thousands of wealthy Londoners, including Nigella Lawson, Kate Moss, Jude Law and Roman Abramovich, have commissioned basements to increase living space as the cost of moving has been made prohibitively expensive by stamp duty and rising prices.

Basement extensions have proved hugely unpopular with neighbours as the work can take up to two years to complete. Some extend three or four storeys below pavement level.

But today’s figures show that the headaches do not end when the builders have finally left.

Mark Jones, head of house building standards at the National House Building Council, said: “In recent times we have seen basements once again become a relevant and attractive addition to many houses.

“But as our claims figures and experience show, basement claims by their very nature are difficult to investigate and costly to repair, which can result in significant disruption.”

Basements are generally covered by 10-year warranties and claims are likely to rise — the NHBC figures show that one in 12 of the basements built in 2005/06 have already gone so badly wrong they have resulted in claims.

Around two thirds of the claims are the result of basements not being properly waterproofed — or tanked — allowing water to seep in and cause damage.